Variable permeability tuning device



Nov. 21, 1950 J. w. MILLION, JR

VARIABLE PERMEABILITY TUNING DEVICE Filed Dec. 4, 1945 INVENTOR BY w ATTORNEY Patented Nov. 21, 1950 VARIABLE PERMEABILITY TUNING DEVICE John W. Million, Jr., Indianapolis, Ind., assignor to Radio Corporation of America, a corporation of Delaware Application December 4, 1945, Serial No. 632,726

Claims. 1

- The present invention relates to a variable permeability tuning device of the type comprising a coil wound in the form of a solenoid and an axially movable ferro-magnetic core for varying the coil inductance, such devices being commonly employed in radio receivers and other radio apparatus for tuning signal frequency and other circuits to resonance,

An object of the invention is to provide a permeability tuning device of the type mentioned with guiding means for the core whereby throughout its axial movement the core is in exact concentricity relative to the coil, eflecting thereby a more precise adjustment, and avoiding also undue frictional contact between the core and coil form.

A further object of the invention is to provide a simple and compact device of the type mentioned which embodies also a cylindrical capacitor, the construction being such that the capacitor is varied at the same time that the inductance is varied.

A more specific object of the invention is to provide a permeability tuning device which comprises an inductance coil wound on a tubular insulating form, a fixed metallic rod disposed in predetermined relation with respect to the coil form, a ferro-magnetic core adapted for axial movement within the coil form, the core being provided with an elongated bore which is adapted to receive thefixed rod, a metallic sleevev fitted Within the bore, anda coating of dielectric material interposed between the rod and sleeve, the latter, elements constituting the electrodes of a cylindrical capacitor, which is varid simultaneously with Variation in the coil inductance upon axial movement of the core relative to the coil.

Other objects and advantages of the invention will best be understood by a consideration of the following description taken together with the accompanying drawing, in which:

vFig. 1 is a longitudinal cross-section through a permeability tuning device constructed in accordance with one embodiment of the invention; Fig. 2 is an enlarged cross-sectionalview taken on the line 22 of Fig. 1; v

4 Fig. 4 is a view similar to Fig. 1 showing a device in accordance with another embodiment of the invention; and

Figs. 3 and 5 are schematic circuit diagrams illustrating various uses of the devices shown in Figs. 1 and 4, respectively.

Referring to Fig. 1 there is shown at l a tubular insulating form on which there is wound an inductance coil 2, the inductance of which it is desired to vary. concentrically arranged within the coil form I is a metal rod 3 which is supported at one end within an insulating grommet 4 carried by a bracket 4", the other end of the rod extending into the coil for a substantial distance. At 5 is shown a rod-like ferro-magnetic core which is adapted for axial movement within the coil form I to vary the coil inductance in a manner well-known in the art. The core 5 is formed with a cylindrical elongated bore 6 which is adapted to receive the metal rod 3, and fitted within the bore is a metal sleeve 1, the inner surface of which is coated with a thin coating 8 of insulating material, such as ceramic. By providing a close fit between the rod 3 and the coated metal sleeve 1, the rod forms a guide whereby thecore and coil maintai exact concentricity throughout the core travel, greater accuracy of calibration being obtained thereby. This construction permits also the use of a smaller clearance between the core and the coil form without causing undue friction therebetween.

A rod-like member or wire 9 is screw-threaded into, or otherwise attached to, the end of the core 5 remote from the end which receives the guide rod 3 and serves as the manual operating member for axially adjusting the core with respect to the coil inductance l. The operating member 9 is connected to ground in the usual manner and an electrical connection I0 is provided between said member and the metallic sleeve 1. A second electrical connection II is connected between the metal guide rod 3 and one end [2 of the coil which is adapted for connection to the signal grid [3 of an electron discharge tube l4, as shown in Fig. 3.

The elements constituting the cylindrical capacitor may be variously constructed- For example, instead of forming the thin coating 8 of dielectric material on the inner surface of the metallic sleeve 1, such coating may be formed on the surface of the fixed metallic guide rod 3. Also, instead of the metallic sleeve l, a metallic film deposit may be formed on the inner surface of the bore in which case the coating of dielectric material 8 may be formed on the metal rod 3, as shown in Fig. 4, or else take the form of a cylindrical insulating sleeve fitted within the thus metallized bore.

In the embodiment of Fig. 1, it will be noted, the inductance and capacitance changes are in the same sense, that is, as the inductance is increased or decreased the capacitance is also in--v creased or decreased. An example of the use of a permeability tuner according to this embodi ment is shown in the circuit of Fig. 3, wherein like elements are indicated by the same reference characters as in Fig. 1. The coil 2 and tubular capacitor 3, l constitute a resonant circuit which may be the signal frequency circuit of a radio receiver. By reason of the. simultaneous variation of the circuit constants (inductance and capacitance) in the same sense, the tuning range is extended beyond that obtainable with a variation in either inductance or capacitance alone.

In the embodiment disclosed in Fig. 4, the arrangement is such that the inductance and capacitance changes are in the opposite sense; in other words, an increase or decrease in inductance is accompanied, respectively, by a decrease or increase in capacitance. The construction of Fig. 4 difiers from that of Fig. 1 in that the metal guide rod 3 is positioned almost entirely outside of the coil (or coil form) and is in coaxial relation therewith in contradistincti'on to the concentric arrangement of Fig. l. The dielectric coating 3 is formed on the surface of rod 3. In the position of adjustment shown in Fig. 4, the device is adjusted for maximum capacitance and minimum inductance. As the magnetic core 5 is moved more and more into the coil, the inductance increases towards a maximum. while the capacitance decreases. towards a minimum.

An example of the use of a permeability tuner of the latter construction is shown in Fig. 5. The pair of tunable circuits l5 and iii are capacitively coupled by the tubular capacitor 3, I which is varied simultaneously in the. opposite sense with change in theinductance of circuit It. This provides a variable coupling between the circuits which decreases more rapidly with increasing frequency than with the use of a fixed capacity coupling.

As a further example, a permeability tuner of the invention may be employed in the, radio ire-- quency stage of a broadcast receiver to improve the over-all gain of this stage. The resonance of the primary circuit of this stage is usually fixed at about 300 k. c., somewhat below the received band of 540 to 1600 k. c. This improves the gain at the low frequency end of the band only. By using a variable capacitor the reso- ,n

nance of the primary circuit can be varied. in step with the tuning so that at the high frequency end of the band (1600 k. c.) the primary circuit is tuned to approximately 456-01" 500. k. 0.

While I have shown and described certain preferred embodiments of my invention it will be understood that various modifications and changes will occur to those skilled in the art without departing from the spirit and scope of this invention.

What I claim is:

l. A permeability tuning device comprising a coil of the solenoid type wound on a tubular insulating form, a magnetic core adapted for axial movement within the coil form and provided with an elongated bore, a. fixed metallic rod axially disposed with respect to said bore and adapted to be received therein whereby the rod serves as a guide for the core during its axial movement, a metallic sleeve within the bore, and a thin coating of dielectric material interposed between said rod and sleeve, said latter elements constituting the electrodes of a con,- denser, the capacity of which is varied simultaneously with variation in inductance of the coil upon axial movement of the core relative to the coil.

2. A permeability tuning device as defined in claim 1 wherein the fixed metallic rod is disposed concentrically with respect to the coil form, and the elongated bore is concentrically arranged within the core.

3. A permeability tuning device as defined in claim 1 wherein the fixed metallic rod is disposed externally of and in coaxial relation with respect to the coil form, and the elongated bore is, concentrically arranged within the core.

4. A permeability tuning device as defined in claim 1 wherein the thin coating of dielectric material is formed on the inner surface of the metallic sleeve.

5. A permeability tuning device as defined in claim 1 wherein the thin coating of dielectric material is formed on the outer surface of the fixed metallic rod.

6. A permeability tuning device as defined in claim 1 wherein the metallic sleeve is in the form of a film deposited on the cylindrical surface of the bore and the fixed metallic rod has formed on' its surface a coating of dielectric material.

7. A permeability tuning device as defined in claim 1 wherein the metallic sleeve is in the form of a film deposited on the cylindrical surface of the bore and the dielectric material is in the form of a cylindrical sleeve fitted within the so coated bore.

8. A permeability tuning device comprising a coil of the solenoid type wound on a tubular in.- sulating form, a magnetic core adapted for-axial movement within the coil form and provided with an elongated bore, a fixed metallic. rod disposed within said coil form, said rod being axialiy disposed with respect to said bore and adapted to be received therein whereby the rod serves as, a guide for the core during its axial movement... a metallic sleeve within the. bore, and a thin coating of dielectric material interposed between said rod and sleeve, said latter elements constituting the electrodes. of a condenser, the capacity of which is' varied simultaneously and in the same sense with variation in inductance of the coil upon axial movement of the. core relative to the coil.

9. A permeability tuning device comprising a coil of the solenoid typewound on a tubular insulating form, a magnetic core adapted for axial movementwi'thin the coil form and provided with an elongated bore, a fixed metallic rod disposed externally of, and in coaxial relation with respect to, said coil form, said rod. being axially disposed with respect to said bore and adapted to be received therein whereby the rod serves as a guide for the core during its axial movement, a metallic sleeve within the bore, and a thin coating of dielectric material interposed between said rod and sleeve, saidlatter elements constituting the electrodes of a condenser, the capacity of which is varied simultaneously and in the opposite sense with variation in inductance of the coil upon axial movement of the core relative to the coil.

10. A radio frequency tuning device comprising an inductance coil of the solenoid type, a ferro-magnetic core arranged for longitudinal movement axially within said coil for varying the inductance of said coil, said core having an elongated concentric bore with an electrically conducting surface, a metallic rod coaxially disposed within said bore in spaced relation from said surface, said core being longitudinally movable 5 relative to said rod, dielectric means radially spacing said rod and said surface, structure electrically connecting said rod and said surface as electrodes of a variable capacitor in circuit with said coil.

JOHN W. MILLION, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Case Sept. 19, 1939 Polydorofi Aug. 6, 1940 Fields July 1, 1941 Sands Sept. 9, 1941 Reid Oct. 14, 1941 Sands et al Jan. 4, 1944 Dolberg July 2, 1946 Beetham July 15, 1947 Certificate of Correction Patent No. 2,531,231 November 21, 1950 JOHN W. MILLION, JR.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correctlon as follows:

Column 3, line 39, after the Word with insert decreasing frequently or increases more rapidly with;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oflice. Signed and sealed this 23rd day of January, A. D. 1951.

THOMAS F. MURPHY,

Assistant Gammz'ssz'oner of Patents.

Certificate of Correction Patent No. 2,531,231 November 21, 1950 JOHN W. MILLION, JR.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correctlon as follows:

Column 3, line 39, after the Word with insert decreasing frequently or increases more rapidly with;

and that the said Letters Patent should be read as corrected above, so that the same may conform to the record of the case in the Patent Oflice. Signed and sealed this 23rd day of January, A. D. 1951.

THOMAS F. MURPHY,

Assistant Commissioner of Patents. 

